Mechanisms of female reproductive behavior, especially regarding hormone effects on the lordosis response, are among the best worked out in mammalian brain. Knowledge of its neural circuitry provides a platform for looking with increased detail at cellular mechanisms for this behavior, which is required for reproduction because it allows fertilization by the male. Following extensive analyses of cellular changes following estradiol (E), it now is easier to study cellular changes which underline progesterone (p)-facilitated behavior. Because effects of progesterone on lordosis require new protein synthesis, classical progestin receptors may play a role. We will use steroid autoradiography to look at receptor/behavior correlations as a function of estrogen dose and anti-progestin dose. What proteins do behaviorally important progestin-receiving cells produce? We will use our technique of combining immunocytochemistry with steroid autoradiography to colocalize nuclear progestin receptors and each of several behaviorally relevant neural proteins. Where do progesterone-receiving cells send their axons? We will combine retrograde neuroanatomical techniques with steroid autoradiography in the same tissue to see if progestin-sensitive cells send axons to certain terminal zones, each implicated in lordosis behavior. In vitro single unit electrophysiology is a chemically clean method of investigating hormone effects on hypothalamic neurons. We will look for electrophysiological/behavioral correlations by giving different E or E+P doses in vivo, testing for lordosis, and studying ventromedial hypothalamic single unit responses to behaviorally active peptides and transmitters. Ultrastructural effects of hormones give clues to guide physiological and behavioral experiments. We will use electron microscopy to look at effects of estrogens and progestins on hypothalamic neurons under conditions which allow morphological/behavioral correlations across hormone treatment durations or amounts of receptor site occupation. Hypothalamic neuron axonal terminals in other brain regions will also be examined. We have developed the application of in situ hybridization techniques to brain tissue, for using labeled cDNA to detect specific messenger RNA in individual cell groups. We will use this technique to study hormone effects on ribosomal RNA and messenger RNA levels for LHRH and proenkephalin.